This invention relates to production of polyester textile yarn and is more particularly concerned with drawing and air-jet texturing continuous filament yarn.
Textured yarn of continuous polyester or nylon filaments is produced by a sequence of steps which involve melt-spinning the polymer into filaments, combining filaments into a yarn, drawing the yarn to provide improved tenacity with a suitable low break elongation, and then texturing the yarn, e.g., to have the appearance and feel similar to costlier spun staple textile yarns. FIG. 1 of Gage U.S. Pat. No. 3,433,008 is a schematic representation of this sequence of steps combined in a continuous operation. Conventionally, the spinning and texturing steps are performed in separate operations. The drawing step may be coupled with the texturing step as shown in FIG. 3 of the patent, or drawing may be coupled with spinning as shown in FIG. 4.
As disclosed in Ludewig "Polyester Fibres," English translation, 1971, John Wiley & Sons Ltd., pages 275-276, drawn polyester filaments which have not been set cannot be used for most textile purposes because of their high shrinkage, a boil-off shrinkage of about 8 percent being obtained even when heat is used during the drawing step. For most textile uses the boil-off shrinkage should be less than 3.5 percent.
Texturing can be accomplished by treating yarn in a jet of heated gas as disclosed in Breen and Lauterbach U.S. Pat. No. 3,543,358. As illustrated in FIG. 2 of this patent, the yarn can be drawn and passed directly to a jet texturing device. In Example I a jet device supplied with superheated steam at 575.degree. F (302.degree. C) was used to impart a three-dimensional curvilinear crimp to drawn nylon filaments. When subsequently heat-relaxed in steam, in the test described at column 12, line 52, to column 13, line 25, a high degree of bulk was obtained but the cross-sectional area of the filaments increased 14%, i.e., the filament shrinkage was 14 percent. Example IX gives data for crimping drawn polyethylene terephthalate yarn with a jet device supplied with steam at 495.degree. F (257.degree. C); the results of subsequent heat-relaxing treatment are not given, but the filament shrinkage would be about 8 percent or more.
It has been conventional to melt-spin polyester into yarn at a take-off speed (the puller roll speed for pulling the yarn filaments away from the spinneret) of 500 to 1500 meters per minute. German O.S. Pat. No. 2,204,397 (laid open Aug. 9, 1973) discloses a coupled spinning and drawing process in which polyester yarn is melt-spun at a take-off speed higher than 3000 meters per minute and then drawn at a draw ratio between 1.8x and 1.3x. In the process illustrated with reference to FIG. 1, the drawing step is performed in a steam atmosphere at 145.degree. C. The object of the invention is stated to be to retain the advantages of the customary melt-spinning and subsequent drawing while attaining an increase in the take-off and production speed without influencing the quality of the product. The patent mentions that, in accordance with the state of the art, further treatments may be used to dye, reduce shrinkage, texturize or crimp the yarn filaments, but no details are given.